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Recirculating aquaculture tank production systems: Aquaponics-Integrating fish and plant culture

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Aquaponics, the combined culture of
fish and plants in recirculating sys-
tems, has become increasingly popu-
lar. Now a news group (aquaponics-
request@townsqr.com — type sub-
scribe) on the Internet discusses
many aspects of aquaponics on a
daily basis. Since 1997, a quarterly
periodical (Aquaponics Journal) has
published informative articles, con-
ference announcements and product
advertisements. At least two large
suppliers of aquaculture and/or
hydroponic equipment have intro-
duced aquaponic systems to their
catalogs. Hundreds of school districts
are including aquaponics as a learn-
ing tool in their science curricula. At
least two short courses on aquapon-
ics have been introduced, and the
number of commercial aquaponic
operations, though small, is increas-
ing.
Aquaponic systems are recirculating
aquaculture systems that incorporate
the production of plants without soil.
Recirculating systems are designed
to raise large quantities of fish in rel-
atively small volumes of water by
treating the water to remove toxic
waste products and then reusing it.
In the process of reusing the water
many times, non-toxic nutrients and
organic matter accumulate. These
metabolic by-products need not be
wasted if they are channeled into
secondary crops that have economic
value or in some way benefit the pri-
mary fish production system.
Systems that grow additional crops
by utilizing by-products from the pro-
duction of the primary species are
referred to as integrated systems. If
the secondary crops are aquatic or
terrestrial plants grown in conjunc-
tion with fish, this integrated system
is referred to as an aquaponic system
(Fig. 1).
Plants grow rapidly with dissolved
nutrients that are excreted directly
by fish or generated from the micro-
bial breakdown of fish wastes. In
closed recirculating systems with
very little daily water exchange (less
than 2 percent), dissolved nutrients
accumulate in concentrations similar
to those in hydroponic nutrient solu-
tions. Dissolved nitrogen, in particu-
lar, can occur at very high levels in
recirculating systems. Fish excrete
waste nitrogen, in the form of ammo-
nia, directly into the water through
their gills. Bacteria convert ammonia
to nitrite and then to nitrate (see
SRAC Publication No. 451,
“Recirculating Aquaculture Tank
Production Systems: An Overview of
Critical Considerations”). Ammonia
and nitrite are toxic to fish, but
nitrate is relatively harmless and is
the preferred form of nitrogen for
growing higher plants such as fruit-
ing vegetables.
Aquaponic systems offer several ben-
efits. Dissolved waste nutrients are
recovered by the plants, reducing dis-
charge to the environment and
extending water use (i.e., by remov-
ing dissolved nutrients through plant
uptake, the water exchange rate can
be reduced). Minimizing water
exchange reduces the costs of operat-
ing aquaponic systems in arid cli-
mates and heated greenhouses where
water or heated water is a significant
expense. Having a secondary plant
crop that receives most of its required
VI
PR
November 2006
Revision
SRAC Publication No. 454
1Agricultural Experiment Station, University of the
Virgin Islands
2Department of Wildlife and Fisheries Sciences,
Texas A&M University
3Biological and Agricultural Engineering
Department, North Carolina State University
Recirculating Aquaculture Tank Production
Systems: Aquaponics—Integrating Fish and
Plant Culture
James E. Rakocy1, Michael P. Masser2and Thomas M. Losordo3
Figure 1. Nutrients from red tilapia
produce a valuable crop of leaf let-
tuce in the UVI aquaponic system.
nutrients at no cost improves a sys-
tem’s profit potential. The daily
application of fish feed provides a
steady supply of nutrients to plants
and thereby eliminates the need to
discharge and replace depleted nutri-
ent solutions or adjust nutrient solu-
tions as in hydroponics. The plants
remove nutrients from the culture
water and eliminate the need for
separate and expensive biofilters.
Aquaponic systems require substan-
tially less water quality monitoring
than separate hydroponic or recircu-
lating aquaculture systems. Savings
are also realized by sharing opera-
tional and infrastructural costs such
as pumps, reservoirs, heaters and
alarm systems. In addition, the
intensive, integrated production of
fish and plants requires less land
than ponds and gardens. Aquaponic
systems do require a large capital
investment, moderate energy inputs
and skilled management. Niche mar-
kets may be required for profitabili-
ty.
System design
The design of aquaponic systems
closely mirrors that of recirculating
systems in general, with the addition
of a hydroponic component and the
possible elimination of a separate
biofilter and devices (foam fractiona-
tors) for removing fine and dissolved
solids. Fine solids and dissolved
organic matter generally do not
reach levels that require foam frac-
tionation if aquaponic systems have
the recommended design ratio. The
essential elements of an aquaponic
system are the fish-rearing tank, a
settleable and suspended solids
removal component, a biofilter, a
hydroponic component, and a sump
(Fig. 2).
Effluent from the fish-rearing tank is
treated first to reduce organic matter
in the form of settleable and sus-
pended solids. Next, the culture
water is treated to remove ammonia
and nitrate in a biofilter. Then, water
flows through the hydroponic unit
where some dissolved nutrients are
taken up by plants and additional
ammonia and nitrite are removed by
bacteria growing on the sides of the
tank and the underside of the poly-
styrene sheets (i.e., fixed-film nitrifi-
cation). Finally, water collects in a
reservoir (sump) and is returned to
the rearing tank. The location of the
sump may vary. If elevated hydro-
ponic troughs are used, the sump
can be located after the biofilter and
water would be pumped up to the
troughs and returned by gravity to
the fish-rearing tank.
The system can be configured so
that a portion of the flow is diverted
to a particular treatment unit. For
example, a small side-stream flow
may go to a hydroponic component
after solids are removed, while most
of the water passes through a biofil-
ter and returns to the rearing tank.
The biofilter and hydroponic compo-
nents can be combined by using
plant support media such as gravel
or sand that also functions as biofil-
ter media. Raft hydroponics, which
consists of floating sheets of poly-
styrene and net pots for plant sup-
port, can also provide sufficient
biofiltration if the plant production
area is large enough. Combining
biofiltration with hydroponics is a
desirable goal because eliminating
the expense of a separate biofilter is
one of the main advantages of
aquaponics. An alternative design
combines solids removal, biofiltra-
tion and hydroponics in one unit.
The hydroponic support media (pea
gravel or coarse sand) captures solids
and provides surface area for fixed-
film nitrification, although with this
design it is important not to overload
the unit with suspended solids.
As an example, Figures 3 and 4 show
the commercial-scale aquaponic sys-
tem that has been developed at the
University of the Virgin Islands
(UVI). It employs raft hydroponics.
Fish production
Tilapia is the fish species most com-
monly cultured in aquaponic sys-
tems. Although some aquaponic sys-
tems have used channel catfish,
largemouth bass, crappies, rainbow
trout, pacu, common carp, koi carp,
goldfish, Asian sea bass (barramun-
di) and Murray cod, most commer-
cial systems are used to raise tilapia.
Most freshwater species, which can
tolerate crowding, will do well in
aquaponic systems (including orna-
mental fish). One species reported to
perform poorly is hybrid striped
bass. They cannot tolerate high lev-
els of potassium, which is often sup-
plemented to promote plant growth.
To recover the high capital cost and
operating expenses of aquaponic sys-
tems and earn a profit, both the fish-
rearing and the hydroponic veg-
etable components must be operated
continuously near maximum pro-
duction capacity. The maximum bio-
mass of fish a system can support
without restricting fish growth is
called the critical standing crop.
Operating a system near its critical
standing crop uses space efficiently,
maximizes production and reduces
variation in the daily feed input to
the system, an important factor in
sizing the hydroponic component.
There are three stocking methods
that can maintain fish biomass near
the critical standing crop: sequential
rearing, stock splitting and multiple
rearing units.
Sequential rearing
Sequential rearing involves the cul-
ture of several age groups (multiple
cohorts) of fish in the same rearing
tank. When one age group reaches
marketable size, it is selectively har-
vested with nets and a grading sys-
tem, and an equal number of finger-
lings are immediately restocked in
the same tank. There are three prob-
lems with this system: 1) the period-
ic harvests stress the remaining fish
and could trigger disease outbreaks;
2) stunted fish avoid capture and
accumulate in the system, wasting
space and feed; and 3) it is difficult
Rearing
tank
Solids
removal Biofilter Hydroponic
subsystem Sump
Combined
Combined
Figure 2. Optimum arrangement of aquaponic system components (not to
scale).
ing crop of the initial rearing tank is
reached. The fish are either herded
through a hatch between adjoining
tanks or into “swimways” connect-
ing distant tanks. Multiple rearing
units usually come in modules of
two to four tanks and are connected
to a common filtration system. After
the largest tank is harvested, all of
the remaining groups of fish are
moved to the next largest tank and
the smallest tank is restocked with
fingerlings. A variation of the multi-
ple rearing unit concept is the divi-
sion of a long raceway into compart-
ments with movable screens. As the
fish grow, their compartment is
increased in size and moved closer
to one end of the raceway where
they will eventually be harvested.
These should be cross-flow race-
ways, with influent water entering
the raceway through a series of ports
down one side of the raceway and
effluent water leaving the raceway
through a series of drains down the
other side. This system ensures that
water is uniformly high quality
throughout the length of the race-
way.
Another variation is the use of sever-
al tanks of the same size. Each rear-
ing tank contains a different age
group of fish, but they are not
moved during the production cycle.
This system does not use space effi-
ciently in the early stages of growth,
but the fish are never disturbed and
the labor involved in moving the
fish is eliminated.
A system of four multiple rearing
tanks has been used successfully
with tilapia in the UVI commercial-
scale aquaponic system (Figs. 3 and
5). Production is staggered so one of
to maintain accurate stock records
over time, which leads to a high
degree of management uncertainty
and unpredictable harvests.
Stock splitting
Stock splitting involves stocking very
high densities of fingerlings and peri-
odically splitting the population in
half as the critical standing crop of
the rearing tank is reached. This
method avoids the carryover prob-
lem of stunted fish and improves
stock inventory. However, the moves
can be very stressful on the fish
unless some sort of “swimway” is
installed to connect all the rearing
tanks. The fish can be herded into
the swimway through a hatch in the
wall of a rearing tank and maneu-
vered into another rearing tank by
movable screens. With swimways,
dividing the populations in half
involves some guesswork because
the fish cannot be weighed or count-
ed. An alternative method is to
crowd the fish with screens and
pump them to another tank with a
fish pump.
Multiple rearing units
With multiple rearing units, the
entire population is moved to larger
rearing tanks when the critical stand-
Sump
Clarifier
Filter tanks
Base addition
Degassing
Fish rearing tanks Hydroponic tanks
Effluent line
Return line
The UVI Aquaponic System
Tank dimensions
Rearing tanks: Diameter: 10 ft, Height:
4 ft, Water volume: 2,060 gal each
Clarifiers: Diameter: 6 ft, Height of
cylinder: 4 ft, Depth of cone: 3.6 ft,
Slope: 45º, Water volume: 1,000 gal
Filter and degassing tanks: Length: 6
ft, Width: 2.5 ft, Depth: 2 ft, Water vol-
ume: 185 gal
Hydroponic tanks: Length: 100 ft,
Width: 4 ft, Depth: 16 in, Water volume:
3,000 gal, Growing area: 2,304 ft2
Sump: Diameter: 4 ft, Height: 3 ft,
Water volume: 160 gal
Base addition tank: Diameter: 2 ft,
Height: 3 ft, Water volume: 50 gal
Total system water volume: 29,375
gal
Flow rate: 100 GPM
Water pump: 12hp
Blowers: 112hp (fish) and 1 hp (plants)
Total land area: 18acre
Figure 3. Layout of UVI aquaponic system with tank dimensions and pipe sizes
(not to scale).
Fig. 4. An early model of the UVI
aquaponic system in St. Croix show-
ing the staggered production of leaf
lettuce in six raft hydroponic tanks.
Figure 5. The UVI aquaponic system at
the New Jersey EcoComplex at Rutgers
University. Effluent from four tilapia-
rearing tanks circulates through eight
raft hydroponic tanks, producing toma-
toes and other crops.
Pipe sizes
Pump to rearing tanks: 3 in
Rearing tanks to clarifier: 4 in
Clarifiers to filter tanks: 4 in
Between filter tanks: 6 in
Filter tank to degassing tank: 4 in
Degassing to hydroponic tanks: 6 in
Between hydroponic tanks: 6 in
Hydroponic tanks to sump: 6 in
Sump to pump: 3 in
Pipe to base addition tank 0.75 in
Base addition tank to sump: 1.25 in
the rearing tanks is harvested every
6 weeks. At harvest, the rearing tank
is drained and all of the fish are
removed. The rearing tank is then
refilled with the same water and
immediately restocked with finger-
lings for a 24-week production cycle.
Each circular rearing tank has a
water volume of 2,060 gallons and is
heavily aerated with 22 air diffusers.
The flow rate to all four tanks is 100
gallons/minute, but the flow rate to
individual tanks is apportioned so
that tanks receive a higher flow rate
as the fish grow. The average rearing
tank retention time is 82 minutes.
Annual production has been 9,152
pounds (4.16 mt) for Nile tilapia and
10,516 pounds (4.78 mt) for red
tilapia (Table 1). However, produc-
tion can be increased to 11,000
pounds (5 mt) with close observation
of the ad libitum feeding response.
In general, the critical standing crop
in aquaponic systems should not
exceed 0.50 pound/gallon. This densi-
ty will promote fast growth and effi-
cient feed conversion and reduce
crowding stress that may lead to dis-
ease outbreaks. Pure oxygen is gener-
ally not needed to maintain this den-
sity.
The logistics of working with both
fish and plants can be challenging.
In the UVI system, one rearing tank
is stocked every 6 weeks. Therefore,
it takes 18 weeks to fully stock the
system. If multiple units are used,
fish may be stocked and harvested
as frequently as once a week.
Similarly, staggered crop production
requires frequent seeding, trans-
planting, harvesting and marketing.
Therefore, the goal of the design
process is to reduce labor wherever
possible and make operations as sim-
ple as possible. For example, pur-
chasing four fish-rearing tanks adds
extra expense. One larger tank could
be purchased instead and partially
harvested and partially restocked
every 6 weeks. However, this opera-
tion requires additional labor, which
is a recurring cost and makes man-
agement more complex. In the long
run, having several smaller tanks in
which the fish are not disturbed
until harvest (hence, less mortality
and better growth) will be more cost
effective.
Solids
Most of the fecal waste fish generate
should be removed from the waste
stream before it enters the hydro-
ponic tanks. Other sources of partic-
ulate waste are uneaten feed and
organisms (e.g., bacteria, fungi and
algae) that grow in the system. If this
organic matter accumulates in the
system, it will depress dissolved oxy-
gen (DO) levels as it decays and pro-
duce carbon dioxide and ammonia.
If deep deposits of sludge form, they
will decompose anaerobically (with-
out oxygen) and produce methane
and hydrogen sulfide, which are
very toxic to fish.
Suspended solids have special signifi-
cance in aquaponic systems.
Suspended solids entering the hydro-
ponic component may accumulate
on plant roots and create anaerobic
zones that prevent nutrient uptake
by active transport, a process that
requires oxygen. However, some
accumulation of solids may be bene-
ficial. As solids are decomposed by
microorganisms, inorganic nutrients
essential to plant growth are released
to the water, a process known as
mineralization. Mineralization sup-
plies several essential nutrients.
Without sufficient solids for mineral-
ization, more nutrient supplementa-
tion is required, which increases the
operating expense and management
complexity of the system. However,
it may be possible to minimize or
eliminate the need for nutrient sup-
plementation if fish stocking and
feeding rates are increased relative
to plants. Another benefit of solids is
that the microorganisms that decom-
pose them are antagonistic to plant
root pathogens and help maintain
healthy root growth.
SRAC Publication No. 453
(“Recirculating Aquaculture Tank
Production Systems: A Review of
Component Options”) describes
some of the common devices used to
remove solids from recirculating sys-
tems. These include settling basins,
tube or plate separators, the combi-
nation particle trap and sludge sepa-
rator, centrifugal separators, micro-
screen filters and bead filters.
Sedimentation devices (e.g., settling
basins, tube or plate separators) pri-
marily remove settleable solids
(>100 microns), while filtration
devices (e.g., microscreen filters,
bead filters) remove settleable and
suspended solids. Solids removal
devices vary in regard to efficiency,
solids retention time, effluent charac-
teristics (both solid waste and treated
water) and water consumption rate.
Sand and gravel hydroponic sub-
strates can remove solid waste from
system water. Solids remain in the
system to provide nutrients to plants
through mineralization. With the
high potential of sand and gravel
media to clog, bed tillage or periodic
media replacement may be required.
The use of sand is becoming less
common, but one popular aquaponic
system uses small beds (8 feet by 4
feet) containing pea gravel ranging
from 18to 14inch in diameter. The
hydroponic beds are flooded several
times daily with system water and
then allowed to drain completely,
and the water returned to the rear-
ing tank. During the draining phase,
air is brought into the gravel. The
high oxygen content of air (com-
Table 1. Average production values for male mono-sex Nile and red tilapia in the UVI aquaponic system.
Nile tilapia are stocked at 0.29 fish/gallon (77 fish/m3) and red tilapia are stocked at 0.58 fish/gallon (154
fish/m3).
Harvest weight Initial Final Growth
Harvest weight per unit weight weight rate Survival
Tilapia per tank (lbs) volume (lb/gal) (g/fish) (g/fish) (g/day) (%) FCR
Nile 1,056 (480 kg) 0.51 (61.5 kg/m3) 79.2 813.8 4.4 98.3 1.7
Red 1,212 (551 kg) 0.59 (70.7 kg/m3) 58.8 512.5 2.7 89.9 1.8
pared to water) speeds the decompo-
sition of organic matter in the gravel.
The beds are inoculated with red
worms (Eisenia foetida), which
improve bed aeration and assimilate
organic matter.
Solids removal
The most appropriate device for
solids removal in a particular system
depends primarily on the organic
loading rate (daily feed input and
feces production) and secondarily on
the plant growing area. For example,
if large numbers of fish (high organic
loading) are raised relative to the
plant growing area, a highly efficient
solids removal device, such as a
microscreen drum filter, is desirable.
Microscreen drum filters capture fine
organic particles, which are retained
by the screen for only a few minutes
before backwashing removes them
from the system. In this system, the
dissolved nutrients excreted directly
by the fish or produced by mineral-
ization of very fine particles and dis-
solved organic matter may be suffi-
cient for the size of the plant growing
area. If small amounts of fish (low
organic loading) are raised relative to
the plant growing area, then solids
removal may be unnecessary, as more
mineralization is needed to produce
sufficient nutrients for the plants.
However, un-stabilized solids (solids
that have not undergone microbial
decomposition) should not be allowed
to accumulate on the tank bottom
and form anaerobic zones. A recipro-
cating pea gravel filter (subject to
flood and drain cycles), in which
incoming water is spread evenly over
the entire bed surface, may be the
most appropriate device in this situa-
tion because solids are evenly distrib-
uted in the gravel and exposed to
high oxygen levels (21 percent in air
as compared to 0.0005 to 0.0007 per-
cent in fish culture water) on the
drain cycle. This enhances microbial
activity and increases the mineraliza-
tion rate.
UVI’s commercial-scale aquaponic
system relies on two cylindro-conical
clarifiers to remove settleable solids.
The fiberglass clarifiers have a vol-
ume of 1,000 gallons each. The cylin-
drical portion of the clarifier is situat-
ed above ground and has a central
baffle that is perpendicular to the
incoming water flow (Fig. 6). The
lower conical portion has a 45-degree
slope and is buried below ground. A
drain pipe is connected to the apex of
the cone. The drain pipe rises verti-
cally out of the ground to the middle
of the cylinder and is fitted with a
ball valve. Rearing tank effluent
enters the clarifier just below the
water surface. The incoming water is
deflected upward by a 45-degree pipe
elbow to dissipate the current. As
water flows under the baffle, turbu-
lence diminishes and solids settle on
the sides of the cone. The solids accu-
mulate there and form a thick mat
that eventually rises to the surface of
the clarifier. To prevent this, approxi-
mately 30 male tilapia fingerlings are
required to graze on the clarifier
walls and consolidate solids at the
base of the cone. Solids are removed
from the clarifier three times daily.
Hydrostatic pressure forces solids
through the drain line when the ball
valve is opened. A second, smaller
baffle keeps floating solids from
being discharged to the filter tanks.
The fingerlings serve another pur-
pose. They swim into and through
the drain lines and keep them clean.
Without tilapia, the 4-inch drain lines
would have to be manually cleaned
nearly every day because of bacterial
growth in the drain lines, which con-
stricts water flow. A cylindrical
screen attached to the rearing tank
drain keeps fingerlings from entering
the rearing tank.
The cylindro-conical clarifier removes
approximately 50 percent of the total
particulate solids produced by the
system and primarily removes large
settleable solids. Although fingerlings
are needed for effective clarifier per-
formance, their grazing and swim-
ming activities are also counterpro-
ductive in that they resuspend some
solids, which exit through the clarifi-
er outlet. As fingerlings become larg-
er (>200 g), clarifier performance
diminishes. Therefore, clarifier fish
must be replaced with small finger-
lings (50 g) periodically (once every 4
months).
With clarification as the sole method
of solids removal, large quantities of
solids would be discharged to the
hydroponic component. Therefore,
another treatment stage is needed to
remove re-suspended and fine solids.
In the UVI system, two rectangular
tanks, each with a volume of 185 gal-
lons, are filled with orchard/bird net-
ting and installed after each of the
two clarifiers (Fig. 7). Effluent from
each clarifier flows through a set of
two filter tanks in series. Orchard
netting is effective in removing fine
solids. The filter tanks remove the
remaining 50 percent of total particu-
late solids.
The orchard netting is cleaned once
or twice each week. Before cleaning,
a small sump pump is used to care-
fully return the filter tank water to
the rearing tanks without dislodging
the solids. This process conserves
water and nutrients. The netting is
cleaned with a high-pressure water
spray and the sludge is discharged to
lined holding ponds.
Effluent from the UVI rearing tanks
is highly enriched with dissolved
organic matter, which stimulates the
growth of filamentous bacteria in the
drain line, clarifier and screen tank.
The bacteria appear as translucent,
gelatinous, light tan filaments. Tilapia
consume the bacteria and control its
growth in the drain line and clarifier,
but bacteria do accumulate in the fil-
ter tanks. Without the filter tanks,
the bacteria would overgrow plant
roots. The bacteria do not appear to
be pathogenic, but they do interfere
with the uptake of dissolved oxygen,
water and nutrients, thereby affect-
ing plant growth. The feeding rate to
the system and the flow rate from
A
B
CD
E
Figure 6. Cross-sectional view (not to
scale) of UVI clarifier showing drain
lines from two fish rearing tanks (A),
central baffle (B) and discharge baffle
(C), outlet to filter tanks (D), sludge
drain line (E) and direction of water
flow (arrows).
the rearing tank determine the extent
to which filamentous bacteria grow,
but they can be contained by provid-
ing a sufficient area of orchard net-
ting, either by adjusting screen tank
size or using multiple screen tanks.
In systems with lower organic load-
ing rates (i.e., feeding rates) or lower
water temperature (hence, less bio-
logical activity), filamentous bacteria
diminish and are not a problem.
The organic matter that accumulates
on the orchard netting between
cleanings forms a thick sludge.
Anaerobic conditions develop in the
sludge, which leads to the formation
of gases such as hydrogen sulfide,
methane and nitrogen. Therefore, a
degassing tank is used in the UVI
system to receive the effluent from
the filter tanks (Fig. 7). A number of
air diffusers vent the gasses into the
atmosphere before the culture water
reaches the hydroponic plants. The
degassing tank has an internal stand-
pipe well that splits the water flow
into three sets of hydroponic tanks.
Solids discharged from aquaponic
systems must be disposed of appro-
priately. There are several methods
for effluent treatment and disposal.
Effluent can be stored in aerated
ponds and applied as relatively dilute
sludge to land after the organic mat-
ter in it has stabilized. This method is
advantageous in dry areas where
sludge can be used to irrigate and fer-
tilize field crops. The solid fraction of
sludge can be separated from water
and used with other waste products
from the system (vegetable matter) to
form compost. Urban facilities might
have to discharge solid waste into
sewer lines for treatment and dispos-
al at the municipal wastewater treat-
ment plant.
Biofiltration
A major concern in aquaponic sys-
tems is the removal of ammonia, a
metabolic waste product excreted
through the gills of fish. Ammonia
will accumulate and reach toxic lev-
els unless it is removed by the
process of nitrification (referred to
more generally as biofiltration), in
which ammonia is oxidized first to
nitrite, which is toxic, and then to
nitrate, which is relatively non-toxic.
Two groups of naturally occurring
bacteria (Nitrosomonas and
Nitrobacter) mediate this two-step
process. Nitrifying bacteria grow as a
film (referred to as biofilm) on the
surface of inert material or they
adhere to organic particles. Biofilters
contain media with large surface
areas for the growth of nitrifying
bacteria. Aquaponic systems have
used biofilters with sand, gravel,
shells or various plastic media as
substrate. Biofilters perform optimal-
ly at a temperature range of 77 to
86 °F, a pH range of 7.0 to 9.0, satu-
rated DO, low BOD (<20 mg/liter)
and total alkalinity of 100 mg/liter or
more. Nitrification is an acid-produc-
ing process. Therefore, an alkaline
base must be added frequently,
depending on feeding rate, to main-
tain relatively stable pH values.
Some method of removing dead
biofilm is necessary to prevent
media clogging, short circuiting of
water flow, decreasing DO values
and declining biofilter performance.
A discussion of nitrification princi-
ples and a description of various
biofilter designs and operating proce-
dures are given in SRAC Publication
Nos. 451, 452 and 453.
Four major biofilter options (rotating
biological contactors, expandable
media filters, fluidized bed filters
and packed tower filters) are dis-
cussed in SRAC Publication No. 453.
If a separate biofilter is required or if
a combined biofilter (biofiltration
and hydroponic substrate) is used,
the standard equations used to size
biofilters may not apply to aquapon-
ic systems, as additional surface area
is provided by plant roots and a con-
siderable amount of ammonia is
taken up by plants. However, the
contribution of various hydroponic
subsystem designs and plant species
to water treatment in aquaponic
systems has not been studied.
Therefore, aquaponic system biofil-
ters should be sized fairly close to
the recommendations for recirculat-
ing systems.
Nitrification efficiency is affected by
pH. The optimum pH range for nitri-
fication is 7.0 to 9.0, although most
studies indicate that nitrification effi-
ciency is greater at the higher end of
this range (high 8s). Most hydroponic
plants grow best at a pH of 5.8 to
6.2. The acceptable range for hydro-
ponic systems is 5.5 to 6.5. The pH
of a solution affects the solubility of
nutrients, especially trace metals.
Essential nutrients such as iron,
manganese, copper, zinc and boron
are less available to plants at a pH
higher than 7.0, while the solubility
of phosphorus, calcium, magnesium
and molybdenum sharply decreases
at a pH lower than 6.0. Compromise
between nitrification and nutrient
availability is reached in aquaponic
systems by maintaining pH close to
7.0.
Nitrification is most efficient when
water is saturated with DO. The UVI
Figure 7. Components of the UVI aquaponic system at the New Jersey EcoComplex
at Rutgers University.
commercial-scale system maintains
DO levels near 80 percent saturation
(6 to 7 mg/L) by aerating the hydro-
ponic tanks with numerous small air
diffusers (one every 4 feet) distrib-
uted along the long axis of the tanks.
Reciprocating (ebb and flow) gravel
systems expose nitrifying bacteria to
high atmospheric oxygen levels dur-
ing the dewatering phase. The thin
film of water that flows through NFT
(nutrient film technique) channels
absorbs oxygen by diffusion, but
dense plant roots and associated
organic matter can block water flow
and create anaerobic zones, which
precludes the growth of nitrifying
bacteria and further necessitates the
installation of a separate biofilter.
Ideally, aquaponic systems should be
designed so that the hydroponic sub-
system also serves as the biofilter,
which eliminates the capital cost and
operational expense of a separate
biofilter. Granular hydroponic media
such as gravel, sand and perlite pro-
vide sufficient substrate for nitrifying
bacteria and generally serve as the
sole biofilter in some aquaponic sys-
tems, although the media has a ten-
dency to clog. If serious clogging
occurs from organic matter overload-
ing, gravel and sand filters can actu-
ally produce ammonia as organic
matter decays, rather than remove it.
If this occurs, the gravel or sand
must be washed and the system
design must be modified by
installing a solids removal device
before the media, or else the organic
loading rate must be decreased by
stocking fewer fish and reducing
feeding rates.
Raft hydroponics, which consists of
channels (with 1 foot of water depth)
covered by floating sheets of poly-
styrene for plant support, also pro-
vides sufficient nitrification if solids
are removed from the flow before it
reaches the hydroponic component.
The waste treatment capacity of raft
hydroponics is equivalent to a feed-
ing ratio of 180 g of fish feed/m2of
plant growing area/day. (Note: 1 m2
= 10.76 ft2and 454 g = 1 lb.) This is
equivalent to about 1.2 pounds of
feed for each 8-foot x 4-foot sheet of
polystyrene foam. After an initial
acclimation period of 1 month, it is
not necessary to monitor ammonia
and nitrite values in the UVI raft sys-
tem. A significant amount of nitrifi-
cation occurs on the undersides of
the polystyrene sheets, especially in
the areas exposed to strong currents
above air diffusers where the biofilm
is noticeably thicker.
Aquaponic systems using nutrient
film technique (NFT) as the hydro-
ponic component may require a sep-
arate biofilter. NFT consists of nar-
row plastic channels for plant sup-
port with a film of nutrient solution
flowing through them (Fig. 8). The
water volume and surface area of
NFT are considerably smaller than in
raft culture because there is just a
thin film of water and no substantial
side wall area or raft underside sur-
face area for colonization by nitrify-
ing bacteria.
Hydroponic subsystems
A number of hydroponic subsystems
have been used in aquaponics.
Gravel hydroponic subsystems are
common in small operations. To
ensure adequate aeration of plant
roots, gravel beds have been operated
in a reciprocating (ebb and flow)
mode, where the beds are alternately
flooded and drained, or in a non-
flooded state, where culture water is
applied continuously to the base of
the individual plants through small-
diameter plastic tubing. Depending
on its composition, gravel can pro-
vide some nutrients for plant growth
(e.g., calcium is slowly released as
the gravel reacts with acid produced
during nitrification).
Gravel has several negative aspects.
The weight of gravel requires strong
support structures. It is subject to
clogging with suspended solids,
microbial growth and the roots that
remain after harvest. The resulting
reduction in water circulation,
together with the decomposition of
organic matter, leads to the forma-
tion of anaerobic zones that impair
or kill plant roots. The small, plastic
tubes used to irrigate gravel are also
subject to clogging with biological
growth. Moving and cleaning gravel
substrate is difficult because of its
weight. Planting in gravel is also dif-
ficult, and plant stems can be dam-
aged by abrasion in outdoor systems
exposed to wind. Gravel retains very
little water if drained, so a disruption
in flow will lead to the rapid onset of
water stress (wilting). The sturdy
infrastructure required to support
gravel and the potential for clogging
limits the size of gravel beds.
One popular gravel-based aquaponic
system uses pea gravel in small beds
that are irrigated through a distribu-
tion system of PVC pipes over the
gravel surface. Numerous small holes
in the pipes distribute culture water
on the flood cycle. The beds are
allowed to drain completely between
flood cycles. Solids are not removed
from the culture water and organic
matter accumulates, but the beds are
tilled between planting cycles so that
some organic matter can be dis-
lodged and discharged.
Sand has been used as hydroponic
media in aquaponic systems and is
an excellent substrate for plant
growth. In an experimental system,
sand beds (25 feet long by 5 feet
wide by 1.6 feet deep) were con-
structed on slightly sloped ground
covered by polyethylene sheets adja-
cent to in-ground rearing tanks, with
the tank floors sloping to one side. A
pump in the deep end of the rearing
tank was activated for 30 minutes
five times daily to furrow irrigate the
adjacent sand bed. The culture water
percolated through the sand and
returned to the rearing tank. A
coarse grade of sand is needed to
reduce the potential for clogging over
time and some solids should be
removed before irrigation.
Perlite is another media that has
been used in aquaponic systems.
Perlite is placed in shallow alu-
minum trays (3 inches deep) with a
baked enamel finish. The trays vary
from 8 inches to 4 feet wide and can
Figure 8. Using nutrient film technique,
basil is produced in an aquaponic sys-
tem at Bioshelters, Inc. in Amherst,
Massachusetts.
be fabricated to any length, with 20
feet the maximum recommended
length. At intervals of 20 feet, adjoin-
ing trays should be separated by 3
inches or more in elevation so that
water drops to the lower tray and
becomes re-aerated. A slope of 1
inch in 12 feet is needed for water
flow. A small trickle of water enters
at the top of the tray, flows through
the perlite and keeps it moist, and
discharges into a trough at the lower
end. Solids must be removed from
the water before it enters the perlite
tray. Full solids loading will clog the
perlite, form short-circuiting chan-
nels, create anaerobic zones and lead
to non-uniform plant growth.
Shallow perlite trays provide mini-
mal area for root growth and are bet-
ter for smaller plants such as lettuce
and herbs.
Nutrient film technique (NFT) has
been successfully incorporated into a
number of aquaponic systems. NFT
consists of many narrow, plastic
troughs (4 to 6 inches wide) in which
plant roots are exposed to a thin film
of water that flows down the
troughs, delivering water, nutrients
and oxygen to the roots of the plants.
The troughs are lightweight, inex-
pensive and versatile. Troughs can
be mounted over rearing tanks to
efficiently use vertical greenhouse
space. However, this practice is dis-
couraged if it interferes with fish and
plant operations such as harvesting.
High plant density can be main-
tained by adjusting the distance
between troughs to provide opti-
mum plant spacing during the grow-
ing cycle. In aquaponic systems that
use NFT, solids must be removed so
they do not accumulate and kill
roots. With NFT, a disruption in
water flow can lead quickly to wilt-
ing and death. Water is delivered at
one end of the troughs by a PVC
manifold with discharge holes above
each trough; it is collected at the
opposite, down-slope end in an open
channel or large PVC pipe. The use
of microtubes, which are used in
commercial hydroponics, is not rec-
ommended because they will clog.
The holes should be as large as prac-
tical to reduce cleaning frequency.
A floating or raft hydroponic sub-
system is ideal for the cultivation of
leafy green and other types of veg-
etables. The UVI system uses three
sets of two raft hydroponic tanks
that are 100 feet long by 4 feet
wide by 16 inches deep and contain
12 inches of water. The channels
are lined with low-density polyeth-
ylene liners (20 mil thick) and cov-
ered by expanded polystyrene
sheets (rafts) that are 8 feet long by
4 feet wide by 1.5 inches thick. Net
pots are placed in holes in the raft
and just touch the water surface.
Two-inch net pots are generally
used for leafy green plants, while 3-
inch net pots are used for larger
plants such as tomatoes or okra.
Holes of the same size are cut into
the polystyrene sheet. A lip at the
top of the net pot secures it and
keeps it from falling through the
hole into the water. Seedlings are
nursed in a greenhouse and then
placed into net pots. Their roots
grow into the culture water while
their canopy grows above the raft
surface. The system provides maxi-
mum exposure of roots to the cul-
ture water and avoids clogging. The
sheets shield the water from direct
sunlight and maintain lower than
ambient water temperature, which
is a beneficial feature in tropical
systems. A disruption in pumping
does not affect the plant’s water
supply as in gravel, sand and NFT
subsystems. The sheets are easily
moved along the channel to a har-
vesting point where they can be
lifted out of the water and placed
on supports at an elevation that is
comfortable for workers (Fig. 9).
A disadvantage of rafts in an
aquaponic system is that roots are
exposed to harmful organisms asso-
ciated with aquaculture systems. If
tilapia fry gain access to the hydro-
ponic tanks, they consume plant
roots and severely stunt plant
growth, although it is relatively easy
to keep fish from entering by placing
a fine mesh screen at the entry point
of water into the degassing tank.
Similarly, blooms of zooplankton,
especially ostracods, will consume
root hairs and fine roots, retarding
plant growth. Other pests are tad-
poles and snails, which consume
roots and nitrifying bacteria. These
problems can be surmounted by
increasing water agitation to prevent
root colonization by zooplankton and
by stocking some carnivorous fish
such as red ear sunfish (shellcrack-
ers) in hydroponic tanks to prey on
tadpoles and snails.
Sump
Water flows by gravity from gravel,
sand and raft hydroponic subsystems
to a sump, which is the lowest point
in the system. The sump contains a
pump or pump inlet that returns the
treated culture water to the rearing
tanks. If NFT troughs or perlite trays
are located above the rearing tanks,
the sump would be positioned in
front of them so that water could be
pumped up to the hydroponic com-
ponent for gravity return to the rear-
ing tanks. There should be only one
pump to circulate water in an
aquaponic system.
The sump should be the only tank
in the system where the water
level decreases as a result of over-
all water loss from evaporation,
transpiration, sludge removal and
splashing. An electrical or mechan-
ical valve is used to automatically
add replacement water from a stor-
age reservoir or well. Municipal
water should not be used unless it
is de-chlorinated. Surface water
should not be used because it may
contain disease organisms. A water
meter should be used to record
additions. Unusually high water
consumption indicates a leak.
The sump is a good location for the
addition of base to the system.
Soluble base such as potassium
hydroxide causes high and toxic pH
levels in the sump. However, as
water is pumped into the rearing
tank, it is diluted and pH decreases
to acceptable levels.
Figure 9. Leaf lettuce being harvested
from a raft hydroponic tank in the UVI
aquaponic system in St. Croix.
The UVI system has a separate base
addition tank located next to the
sump. As water is pumped from the
sump to the fish-rearing tanks, a
small pipe, tapped into the main
water distribution line, delivers a
small flow of water to the base addi-
tion tank, which is well aerated with
one large air diffuser. When base is
added to this tank and dissolves, the
resulting high pH water slowly flows
by gravity into the sump, where it is
rapidly diluted and pumped to fish-
rearing tanks. This system prevents a
rapid pH increase in the fish-rearing
tank.
Construction materials
Many materials can be used to con-
struct aquaponic systems. Budget
limitations often lead to the selection
of inexpensive and questionable
materials such as vinyl-lined, steel-
walled swimming pools. Plasticizers
used in vinyl manufacture are toxic
to fish, so these liners must be
washed thoroughly or aged with
water for several weeks before fish
can be added safely to a tank of clean
water. After a few growing periods,
vinyl liners shrink upon drying,
become brittle and crack, while the
steel walls gradually rust. Nylon-rein-
forced, neoprene rubber liners are
not recommended either. Tilapia eat
holes in rubber liners at the folds as
they graze on microorganisms.
Moreover, neoprene rubber liners are
not impervious to chemicals. If herbi-
cides and soil sterilants are applied
under or near rubber liners, these
chemicals can diffuse into culture
water, accumulate in fish tissue and
kill hydroponic vegetables.
Fiberglass is the best construction
material for rearing tanks, sumps and
filter tanks. Fiberglass tanks are stur-
dy, durable, non-toxic, movable and
easy to plumb. Polyethylene tanks are
also very popular for fish rearing and
gravel hydroponics because of their
low cost. NFT troughs made from
extruded polyethylene are specifically
designed to prevent the puddling and
water stagnation that lead to root
death and are preferable to makeshift
structures such as PVC pipes. Plastic
troughs are commercially available
for floating hydroponic subsystems,
but they are expensive. A good alter-
native is the 20-mil polyethylene lin-
ers that are placed inside concrete-
block or poured-concrete side walls.
They are easy to install, relatively
inexpensive and durable, with an
expected life of 12 to 15 years. A soil
floor covered with fine sand will pre-
vent sharp objects from puncturing
the liners. Lined hydroponic tanks
can be constructed to very large
sizes—hundreds of feet long and up
to 30 feet wide.
Component ratios
Aquaponic systems are generally
designed to meet the size require-
ments for solids removal (for those
systems requiring solids removal)
and biofiltration (if a separate biofil-
ter is used) for the quantity of fish
being raised (see SRAC Publication
No. 453, “Recirculating Aquaculture
Tank Production Systems: A Review
of Component Options”). After the
size requirements are calculated, it is
prudent to add excess capacity as a
safety margin. However, if a separate
biofilter is used, the hydroponic
component is the safety factor
because a significant amount of
ammonia uptake and nitrification
will occur regardless of hydroponic
technique.
Another key design criterion is the
ratio between the fish-rearing and
hydroponic components. The key is
the ratio of daily feed input to plant
growing area. If the ratio of daily
feeding rate to plants is too high,
nutrient salts will accumulate rapid-
ly and may reach phytotoxic levels.
Higher water exchange rates will be
required to prevent excessive nutri-
ent buildup. If the ratio of daily
feeding rate to plants is too low,
plants will develop nutrient deficien-
cies and need more nutrient supple-
mentation. Fortunately, hydroponic
plants grow well over a wide range
of nutrient concentrations.
The optimum ratio of daily fish
feed input to plant growing area
will maximize plant production
while maintaining relatively stable
levels of dissolved nutrients. A vol-
ume ratio of 1 ft3of fish-rearing
tank to 2 ft3of pea gravel hydro-
ponic media (18to 14inch in diam-
eter) is recommended for recipro-
cating (flood and drain) gravel
aquaponic systems. This ratio
requires that tilapia be raised to a
final density of 0.5 pound/gallon
and fed appropriately. With the
recommended ratio, no solids are
removed from the system. The
hydroponic beds should be culti-
vated (stirred up) between crops
and inoculated with red worms to
help break down and assimilate
the organic matter. With this sys-
tem, nutrient supplementation
may not be necessary.
As a general guide for raft aquapon-
ics, a ratio in the range of 60 to 100
g of fish feed/m2of plant growing
area per day should be used. Ratios
within this range have been used
successfully in the UVI system for
the production of tilapia, lettuce,
basil and several other plants. In the
UVI system all solids are removed,
with a residence time of <1 day for
settleable solids (>100 micrometers)
removed by a clarifier, and 3 to 7
days for suspended solids removed
by an orchard netting filter. The sys-
tem uses rainwater and requires
supplementation for potassium, cal-
cium and iron.
Another factor to consider in
determining the optimum feeding
rate ratio is the total water volume
of the system, which affects nutri-
ent concentrations. In raft hydro-
ponics, approximately 75 percent
of the system water volume is in
the hydroponic component,
whereas gravel beds and NFT
troughs contain minor amounts of
system water. Theoretically, in
systems producing the same quan-
tity of fish and plants, a daily
feeding rate of 100 g/m2would
produce total nutrient concentra-
tions nearly four times higher in
gravel and NFT systems (e.g.,
1,600 mg/L) than in raft systems
(e.g., 400 mg/L), but total nutrient
mass in the systems would be the
same. Nutrient concentrations out-
side acceptable ranges affect plant
growth. Therefore, the optimum
design ratio varies with the type
of hydroponic component. Gravel
and NFT systems should have a
feeding rate ratio that is approxi-
mately 25 percent of the recom-
mended ratio for raft hydroponics.
Other factors in determining the
optimum feeding rate ratio are the
water exchange rate, nutrient levels
in the source water, degree and
speed of solids removal, and type of
plant being grown. Lower rates of
water exchange, higher source-water
nutrient levels, incomplete or slow
solids removal (resulting in the
release of more dissolved nutrients
through mineralization), and slow-
growing plants would allow a lower
feeding rate ratio. Conversely, higher
water exchange rates, low source-
water nutrient levels, rapid and com-
plete solids removal, and fast-grow-
ing plants would allow a higher
feeding rate ratio.
The optimum feeding rate ratio is
influenced by the plant culture
method. With batch culture, all
plants in the system are planted and
harvested at the same time. During
their maximum growth phase, there
is a large uptake of nutrients, which
requires a higher feeding rate ratio
during that period. In practice, how-
ever, a higher feeding rate ratio is
used throughout the production
cycle. With a staggered production
system, plants are in different stages
of growth, which levels out nutrient
uptake rates and allows good pro-
duction with slightly lower feeding
rate ratios.
In properly designed aquaponic sys-
tems, the surface area of the hydro-
ponic component is large compared
to the surface area of the fish-rearing
tank (stocked at commercially rele-
vant densities). The commercial-
scale unit at UVI has a ratio of 7.3:1.
The total plant growing area is 2,304
ft2and the total fish-rearing surface
area is 314 ft2.
Plant growth requirements
For maximum growth, plants in
aquaponic systems require 16 essen-
tial nutrients. These are listed below
in the order of their concentrations
in plant tissue, with carbon and oxy-
gen being the highest. The essential
elements are arbitrarily divided into
macronutrients, those required in
relatively large quantities, and
micronutrients, those required in
considerably smaller amounts. Three
of the macronutrients—carbon (C),
oxygen (O) and hydrogen (H)—are
supplied by water (H2O) and carbon
dioxide gas (CO2). The remaining
nutrients are absorbed from the cul-
ture water. Other macronutrients
include nitrogen (N), potassium (K),
calcium (Ca), magnesium (Mg),
phosphorus (P) and sulfur (S). The
seven micronutrients include chlo-
rine (Cl), iron (Fe), manganese (Mn),
boron (B), zinc (Zn), copper (Cu) and
molybdenum (Mo). These nutrients
must be balanced for optimum plant
growth. High levels of one nutrient
can influence the bioavailability of
others. For example, excessive
amounts of potassium may interfere
with the uptake of magnesium or
calcium, while excessive amounts of
either of the latter nutrients may
interfere with the uptake of the
other two nutrients.
Enriching the air in an unventilated
greenhouse with CO2has dramati-
cally increased crop yields in north-
ern latitudes. Doubling atmospheric
CO2increases agricultural yields by
an average of 30 percent. However,
the high cost of energy to generate
CO2has discouraged its use. An
aquaponic system in a tightly
enclosed greenhouse is ideal because
CO2is constantly vented from the
culture water.
There is a growing body of evidence
that healthy plant development
relies on a wide range of organic
compounds in the root environment.
These compounds, generated by
complex biological processes involv-
ing microbial decomposition of
organic matter, include vitamins,
auxins, gibberellins, antibiotics,
enzymes, coenzymes, amino acids,
organic acids, hormones and other
metabolites. Directly absorbed and
assimilated by plants, these com-
pounds stimulate growth, enhance
yields, increase vitamin and mineral
content, improve fruit flavor and
hinder the development of
pathogens. Various fractions of dis-
solved organic matter (e.g., humic
acid) form organo-metallic complex-
es with Fe, Mn and Zn, thereby
increasing the availability of these
micronutrients to plants. Although
inorganic nutrients give plants an
avenue to survival, plants not only
use organic metabolites from the
environment, but also need these
metabolites to reach their full
growth potential.
Maintaining high DO levels in the
culture water is extremely important
for optimal plant growth, especially
in aquaponic systems with their
high organic loads. Hydroponic
plants are subject to intense root res-
piration and draw large amounts of
oxygen from the surrounding water.
If DO is deficient, root respiration
decreases. This reduces water
absorption, decreases nutrient
uptake, and causes the loss of cell
tissue from roots. The result is
reduced plant growth. Low DO lev-
els correspond with high concentra-
tions of carbon dioxide, a condition
that promotes the development of
plant root pathogens. Root respira-
tion, root growth and transpiration
are greatest at saturated DO levels.
Climatic factors also are important
for hydroponic plant production.
Production is generally best in
regions with maximum intensity
and daily duration of light. Growth
slows substantially in temperate
greenhouses during winter because
solar radiation is low. Supplemental
illumination can improve winter
production, but is not generally cost
effective unless an inexpensive ener-
gy source is available.
Water temperature is far more
important than air temperature for
hydroponic plant production. The
best water temperature for most
hydroponic crops is about 75 °F.
However, water temperature can go
as low as the mid-60s for most com-
mon garden crops and slightly lower
for winter crops such as cabbage,
brussel sprouts and broccoli.
Maintaining the best water tempera-
ture requires heating during the
winter in temperate greenhouses
and year-round cooling in tropical
greenhouses. In addition to evapora-
tive cooling of tropical greenhouses,
chillers are often used to cool the
nutrient solution. In tropical outdoor
systems, complete shading of the
fish-rearing and filtration compo-
nents lowers system water tempera-
ture. In raft hydroponics, the poly-
styrene sheets shield water from
direct sunlight and maintain temper-
atures that are several degrees lower
than those in open bodies of water.
Crop varieties may need to be
adjusted seasonally for both temper-
ate and tropical aquaponic produc-
tion. Plants cultured in outdoor
aquaponic systems must be protect-
ed from strong winds, especially
after transplanting when seedlings
are fragile and most vulnerable to
damage.
Nutrient dynamics
Dissolved nutrients are measured
collectively as total dissolved solids
(TDS), expressed as ppm, or as the
capacity of the nutrient solution to
conduct an electrical current (EC),
expressed as millimhos/cm
(mmho/cm). In a hydroponic solu-
tion, the recommended range for
TDS is 1,000 to 1,500 ppm (1.5 to 3.5
mmho/cm). In an aquaponic system,
considerably lower levels of TDS
(200 to 400 ppm) or EC (0.3 to 0.6
mmho/cm) will produce good results
because nutrients are generated con-
tinuously. A concern with aquaponic
systems is nutrient accumulation.
High feeding rates, low water
exchange and insufficient plant
growing areas can lead to the rapid
buildup of dissolved nutrients to
potentially phytotoxic levels.
Phytotoxicity occurs at TDS concen-
trations above 2,000 ppm or EC
above 3.5 mmho/cm. Because
aquaponic systems have variable
environmental conditions such as
daily feed input, solids retention,
mineralization, water exchange,
nutrient input from source water or
supplementation, and variable nutri-
ent uptake by different plant species,
it is difficult to predict the exact level
of TDS or EC and how it is chang-
ing. Therefore, the culturist should
purchase an inexpensive conductivi-
ty meter and periodically measure
TDS or EC. If dissolved nutrients are
steadily increasing and approach
2,000 ppm as TDS or 3.5 mmho/cm
as EC, increasing the water exchange
rate or reducing the fish stocking
rate and feed input will quickly
reduce nutrient accumulation.
However, because these methods
either increase costs (i.e., more water
consumed) or lower output (i.e., less
fish produced), they are not good
long-term solutions. Better but more
costly solutions involve removing
more solids (i.e., upgrade the solids
removal component) or enlarging
the plant-growing areas.
The major ions that increase conduc-
tivity are nitrate (NO3-), phosphate
(PO4-2), sulfate (SO4-2), K+, Ca+2 and
Mg+2. Levels of NO3-, PO4-2 and SO4-2
are usually sufficient for good plant
growth, while levels of K+and Ca+2
are generally insufficient. Potassium
is added to the system in the form of
potassium hydroxide (KOH) and Ca
is added as calcium hydroxide
[Ca(OH)2]. In the UVI commercial-
scale system, KOH and Ca(OH)2are
added in equal amounts (usually 500
to 1,000 g). The bases are added
alternately several times weekly to
maintain pH near 7.0. Adding basic
compounds of K and Ca serves the
dual purpose of supplementing
essential nutrients and neutralizing
acid. In some systems Mg also may
be limiting. Magnesium can be sup-
plemented by using dolomite
[CaMg(CO3)2] as the base to adjust
pH. The addition of too much Ca
can cause phosphorous to precipitate
from culture water in the form of
dicalcium phosphate [CaHPO4].
Sodium bicarbonate (NaHCO3)
should never be added to an
aquaponic system for pH control
because a high Na+level in the pres-
ence of chloride is toxic to plants.
The Na+concentration in hydropon-
ic nutrient solutions should not
exceed 50 mg/L. Higher Na+levels
will interfere with the uptake of K+
and Ca+2. In lettuce, reduced Ca+2
uptake causes tip-burn, resulting in
an unmarketable plant. Tip-burn
often occurs during the warmer
months. Salt (NaCl) is added to fish
feed during manufacture. A produc-
er who orders large quantities of
feed could request that salt not be
added if this does not affect fish
health. If Na+exceeds 50 mg/L and
the plants appear to be affected, a
partial water exchange (dilution)
may be necessary. Rainwater is used
in UVI’s systems because the
groundwater of semiarid islands gen-
erally contains too much salt for
aquaponics.
The accumulation of too much
nitrate in aquaponic systems is
sometimes a concern as fruiting
plants set less fruit and produce
excess vegetative growth when
nitrate levels are high. The filter
tanks in the UVI commercial-scale
system have a mechanism for con-
trolling nitrate levels through denitri-
fication, the reduction of nitrate ions
to nitrogen gas by anaerobic bacte-
ria. Large quantities of organic mat-
ter accumulate on the orchard net-
ting between cleanings. Denitrifica-
tion occurs in anaerobic pockets that
develop in the sludge. Water moves
through the accumulated sludge,
which provides good contact
between nitrate ions and denitrifying
bacteria. The frequency of cleaning
the netting regulates the degree of
denitrification. When the netting is
cleaned often (e.g., twice per week),
sludge accumulation and denitrifica-
tion are minimized, which leads to
an increase in nitrate concentrations.
When the netting is cleaned less
often (e.g., once per week), sludge
accumulation and denitrification are
maximized, which leads to a
decrease in nitrate levels. Nitrate-
nitrogen levels can be regulated
within a range of 1 to 100 mg/L or
more. High nitrate concentrations
promote the growth of leafy green
vegetables, while low nitrate concen-
trations promote fruit development
in vegetables such as tomatoes.
The micronutrients Fe+2, Mn+2,
Cu+2, B+3 and Mo+6 do not accumu-
late significantly in aquaponic sys-
tems with respect to cumulative feed
input. The Fe+2 derived from fish
feed is insufficient for hydroponic
vegetable production and must be
supplemented with chelated Fe+2 so
that the concentration of Fe+2 is 2.0
mg/L. Chelated Fe+2 has an organic
compound attached to the metal ion
to prevent it from precipitating out
of solution and making it unavailable
to plants. The best chelate is Fe-
DTPA because it remains soluble at
pH 7.0. Fe-EDTA is commonly used
in the hydroponics industry, but it is
less stable at pH 7.0 and needs to be
replenished frequently. Fe+2 also can
be applied in a foliar spray directly
to plant leaves. A comparison of
Mn+2, B+3 and Mo+6 levels with
standard nutrient formulations for
lettuce shows that their concentra-
tions in aquaponic systems are sev-
eral times lower than their initial lev-
els in hydroponic formulations.
Deficiency symptoms for Mn+2, B+3
and Mo+6 are not detected in
aquaponic systems, so their concen-
trations appear to be adequate for
normal plant growth. Concentrations
of Cu+2 are similar in aquaponic sys-
tems and hydroponic formulations,
while Zn+2 accumulates in aquapon-
ic systems to levels that are four to
sixteen times higher than initial lev-
els in hydroponic formulations.
Nevertheless, Zn+2 concentrations
usually remain within the limit that
is safe for fish.
Vegetable selection
Many types of vegetables have been
grown in aquaponic systems.
However, the goal is to culture a veg-
etable that will generate the highest
level of income per unit area per
unit time. With this criterion, culi-
nary herbs are the best choice. They
grow very rapidly and command
high market prices. The income
from herbs such as basil, cilantro,
chives, parsley, portulaca and mint is
much higher than that from fruiting
crops such as tomatoes, cucumbers,
eggplant and okra. For example, in
experiments in UVI’s commercial-
scale system, basil production was
11,000 pounds annually at a value of
$110,000, compared to okra produc-
tion of 6,400 pounds annually at a
value of $6,400. Fruiting crops also
require longer culture periods (90
days or more) and have more pest
problems and diseases. Lettuce is
another good crop for aquaponic sys-
tems because it can be produced in a
short period (3 to 4 weeks in the sys-
tem) and, as a consequence, has rela-
tively few pest problems. Unlike
fruiting crops, a large portion of the
harvested biomass is edible. Other
suitable crops are Swiss chard, pak
choi, Chinese cabbage, collard and
watercress. The cultivation of flow-
ers has potential in aquaponic sys-
tems. Good results have been
obtained with marigold and zinnia in
UVI’s aquaponic system. Traditional
medicinal plants and plants used for
the extraction of modern pharmaceu-
ticals have not been cultivated in
aquaponic systems, but there may be
potential for growing some of these
plants. All plant production has to be
coupled to the producer’s ability to
market the final product.
Crop production systems
There are three strategies for pro-
ducing vegetable crops in the hydro-
ponic component. These are stag-
gered cropping, batch cropping and
intercropping. A staggered crop pro-
duction system is one in which
groups of plants in different stages
of growth are cultivated simultane-
ously. This allows produce to be har-
vested regularly and keeps the
uptake of nutrients from the culture
water relatively constant. This sys-
tem is most effective where crops
can be grown continuously, as in the
tropics, subtropics, or temperate
greenhouses with environmental
control. At UVI, the production of
leaf lettuce is staggered so that a
crop can be harvested weekly on
the same day, which facilitates mar-
keting arrangements. Bibb lettuce
reaches market size 3 weeks after
transplanting. Therefore, three
growth stages of Bibb lettuce are
cultivated simultaneously, and one-
third of the crop is harvested week-
ly. Red leaf lettuce and green leaf
lettuce require 4 weeks to reach
marketable size. The cultivation of
four growth stages of these lettuce
varieties allows one-fourth of the
crop to be harvested weekly. In 3
years of continuous operation, UVI
has harvested 148 crops of lettuce,
which demonstrates the system’s
sustainability. Leafy green vegeta-
bles, herbs and other crops with
short production periods are well
suited for continuous, staggered pro-
duction systems.
A batch cropping system is more
appropriate for crops that are grown
seasonally or have long growing
periods (>3 months), such as toma-
toes and cucumbers. Various inter-
cropping systems can be used in
conjunction with batch cropping.
For example, if lettuce is inter-
cropped with tomatoes and cucum-
bers, one crop of lettuce can be har-
vested before the tomato plant
canopy begins to limit light.
Pest and disease control
Pesticides should not be used to con-
trol insects on aquaponic plant
crops. Even pesticides that are regis-
tered would pose a threat to fish and
would not be permitted in a fish cul-
ture system. Similarly, therapeutants
for treating fish parasites and dis-
eases should not be used because
vegetables may absorb and concen-
trate them. The common practice of
adding salt to treat fish diseases or
reduce nitrite toxicity is detrimental
to plant crops. Nonchemical meth-
ods of integrated pest management
must be used. These include biologi-
cal control (resistant cultivars, preda-
tors, pathogens, antagonistic organ-
isms), physical barriers, traps, and
manipulation of the physical envi-
ronment. There are more opportuni-
ties to use biological control meth-
ods in enclosed greenhouse environ-
ments than in exterior installations.
Parasitic wasps and ladybugs can be
used to control white flies and
aphids. In UVI’s systems, caterpil-
lars are effectively controlled by
twice weekly spraying with Bacillus
thuringiensis, a bacterial pathogen
that is specific to caterpillars. Fungal
root pathogens (Pythium), which are
encountered in summer at UVI and
reduce production, dissipate in win-
ter in response to lower water tem-
perature.
The prohibition on the use of pesti-
cides makes crop production in
aquaponic systems more difficult.
However, this restriction ensures
that crops from aquaponic systems
will be raised in an environmentally
sound manner and be free of pesti-
cide residues. A major advantage of
aquaponic systems is that crops are
less susceptible to attack from soil-
borne diseases. Plants grown in
aquaponic systems may be more
resistant to diseases that affect plants
grown in standard hydroponics. This
resistance may be due to the pres-
ence of some organic matter in the
culture water that creates a stable
growing environment with a wide
diversity of microorganisms, some of
which may be antagonistic to plant
root pathogens (Fig. 10).
Approaches to system design
There are several ways to design an
aquaponic system. The simplest
approach is to duplicate a standard
system or scale a standard system
down or up, keeping the compo-
nents proportional. Changing aspects
of the standard design is not recom-
mended because changes often lead
to unintended consequences. How-
ever, the design process often starts
with a production goal for either fish
or plants. In those cases there are
some guidelines that can be fol-
lowed.
Use an aquaponic system that is
already designed. The easiest
approach is to use a system design
that has been tested and is in com-
mon use with a good track record. It
is early in the development of
aquaponics, but standard designs will
emerge. The UVI system has been
well documented and is being stud-
ied or used commercially in several
locations, but there are other systems
with potential. Standard designs will
include specifications for layout, tank
sizes, pipe sizes, pipe placement,
pumping rates, aeration rates, infra-
structure needs, etc. There will be
operation manuals and projected pro-
duction levels and budgets for vari-
ous crops. Using a standard design
will reduce risk.
Design for available space. If a limited
amount of space is available, as in an
existing greenhouse, then that space
will define the size of the aquaponic
system. A standard design can be
scaled down to fit the space. If a
scaled-down tank or pipe size falls
between commercially available
sizes, it is best to select the larger
size. However, the water flow rate
should equal the scaled-down rate
for best results. The desired flow rate
can be obtained by buying a higher
capacity pump and installing a
bypass line and valve, which circu-
lates a portion of the flow back to
the sump and allows the desired
flow rate to go from the pump to the
next stage of the system. If more
space is available than the standard
design requires, then the system
could be scaled up within limitations
or more than one scaled-down sys-
tem could be installed.
Design for fish production. If the pri-
mary objective is to produce a cer-
tain amount of fish annually, the first
step in the design process will be to
determine the number of systems
required, the number of rearing
tanks required per system, and the
optimum rearing tank size. The num-
ber of harvests will have to be calcu-
lated based on the length of the cul-
ture period. Assume that the final
density is 0.5 pound/gallon for an
aerated system. Take the annual pro-
duction per system and multiply it
by the estimated feed conversion
ratio (the pounds of feed required to
produce 1 pound of fish). Convert
the pounds of annual feed consump-
tion to grams (454 g/lb) and divide by
365 days to obtain the average daily
feeding rate. Divide the average daily
feeding rate by the desired feeding
rate ratio, which ranges from 60 to
100 g/m2/day for raft culture, to
determine the required plant produc-
tion area. For other systems such as
NFT, the feeding rate ratio should be
decreased in proportion to the water
volume reduction of the system as
discussed in the component ratio sec-
tion. Use a ratio near the low end of
the range for small plants such as
Bibb lettuce and a ratio near the high
end of the range for larger plants
such as Chinese cabbage or romaine
lettuce. The solids removal compo-
nent, water pump and blowers
should be sized accordingly
Sample problem:
This example illustrates only the
main calculations, which are simpli-
fied (e.g., mortality is not considered)
for the sake of clarity. Assume that
you have a market for 500 pounds of
live tilapia per week in your city and
that you want to raise lettuce with
the tilapia because there is a good
market for green leaf lettuce in your
area. The key questions are: How
many UVI aquaponic systems do
you need to harvest 500 pounds of
tilapia weekly? How large should the
rearing tanks be? What is the appro-
priate number and size of hydroponic
tanks? What would the weekly let-
tuce harvest be?
1. Each UVI system contains four
fish-rearing tanks (Fig. 3). Fish
production is staggered so that
one fish tank is harvested every 6
weeks. The total growing period
per tank is 24 weeks. If 500
pounds of fish are required
weekly, six production systems
(24 fish-rearing tanks) are need-
ed.
2. Aquaponic systems are designed
to achieve a final density of 0.5
pound/gallon. Therefore, the
water volume of the rearing
tanks is 1,000 gallons.
3. In 52 weeks, there will be 8.7
harvests (52 ÷ 6 = 8.7) per sys-
tem. Annual production for the
system, therefore, is 4,350
pounds (500 pounds per harvest
×8.7 harvests).
4. The usual feed conversion ratio
is 1.7. Therefore, annual feed
input to the system is 7,395
pounds (4,350 lb ×1.7 = 7,395
lb).
5. The average daily feed input is
20.3 pounds (7,395 lb/year ÷ 365
days = 20.3 lb).
6. The average daily feed input con-
verted to grams is 9,216 g (20.3
lb ×454 g/lb = 9216 g).
7. The optimum feeding rate ratio
for raft aquaponics ranges from
60 to 100 g/m2/day. Select 80
g/m2/day as the design ratio.
Therefore, the required lettuce
growing area is 115.2 m2(9,216
g/day ÷ 80 g/m2/day =115.2 m2).
8. The growing area in square feet
is 1,240 (115.2 m2×10.76 ft2/m2
= 1,240 ft2).
9. Select a hydroponic tank width
of 4 feet. The total length of the
hydroponic tanks is 310 feet
(1,240 ft2÷ 4 ft = 310 ft).
10. Select four hydroponic tanks.
They are 77.5 feet long (310 ft ÷
4 = 77.5 ft). They are rounded
up to 80 feet in length, which is
a practical length for a standard
greenhouse and allows the use of
ten 8-foot sheets of polystyrene
per hydroponic tank.
11. Green leaf lettuce produces
Figure 10. Healthy roots of Italian pars-
ley cultured on rafts in a UVI aquapon-
ic system at the Crop Diversification
Center South in Alberta, Canada.
good results with plant spacing
of 48 plants per sheet (16/m2).
The plants require a 4-week
growth period. With staggered
production, one hydroponic tank
is harvested weekly. Each hydro-
ponic tank with ten polystyrene
sheets produces 480 plants. With
six aquaponic production sys-
tems 2,880 plants are harvested
weekly.
In summary, the weekly production
of 500 pounds of tilapia results in
the production of 2,880 green leaf
lettuce plants (120 cases). Six
aquaponic systems, each with four
1,000-gallon rearing tanks (water vol-
ume), are required. Each system will
have four raft hydroponic tanks that
are 80 feet long by 4 feet wide.
Design for plant production. If the pri-
mary objective is to produce a cer-
tain quantity of plant crops annually,
the first step in the design process
will be to determine the area
required for plant production. The
area needed will be based on plant
spacing, length of the production
cycle, number of crops per year or
growing season, and the estimated
yield per unit area and per crop
cycle. Select the desired feeding rate
ratio and multiple by the total area
to obtain the average daily feeding
rate required. Multiply the average
daily feeding rate by 365 days to
determine annual feed consumption.
Estimate the feed conversion ratio
(FCR) for the fish species that will be
cultured. Convert FCR to feed con-
version efficiency. For example, if
FCR is 1.7:1, then the feed conver-
sion efficiency is 1 divided by 1.7 or
0.59. Multiply the annual feed con-
sumption by the feed conversion
efficiency to determine net annual
fish yield. Estimate the average fish
weight at harvest and subtract the
anticipated average fingerling weight
at stocking. Divide this number into
the net annual yield to determine the
total number of fish produced annu-
ally. Multiply the total number of
fish produced annually by the esti-
mated harvest weight to determine
total annual fish production. Divide
total annual fish production by the
number of production cycles per
year. Take this number and divide by
0.5 pound/gallon to determine the
total volume that must be devoted to
fish production. The required water
volume can be partitioned among
multiple systems and multiple tanks
per system with the goal of creating
a practical system size and tank
array. Divide the desired individual
fish weight at harvest by 0.5
pound/gallon to determine the vol-
ume of water (in gallons) required
per fish. Divide the number of gal-
lons required per fish by the water
volume of the rearing tank to deter-
mine the fish stocking rate. Increase
this number by 5 to 10 percent to
allow for expected mortality during
the production cycle. The solids
removal component, water pump
and blowers should be sized accord-
ingly.
Sample problem:
Assume that there is a market for
1,000 Bibb lettuce plants weekly in
your city. These plants will be sold
individually in clear, plastic,
clamshell containers. A portion of
the root mass will be left intact to
extend self life. Bibb lettuce trans-
plants are cultured in a UVI raft sys-
tem for 3 weeks at a density of 29.3
plants/m2. Assume that tilapia will
be grown in this system. The key
questions are: How large should the
plant growing area be? What will be
the annual production of tilapia?
How large should the fish-rearing
tanks be?
1. Bibb lettuce production will be
staggered so that 1,000 plants
can be harvested weekly.
Therefore, with a 3-week grow-
ing period, the system must
accommodate the culture of
3,000 plants.
2. At a density of 29.3 plants/m2,
the total plant growing area will
be 102.3 m2(3,000 plants ÷
29.3/m2= 102.3 m2). This area
is equal to 1,100 square feet
(102.3 m2×10.76 ft2/m2= 1,100
ft2).
3. Select a hydroponic tank width
of 8 feet. The total hydroponic
tank length will be 137.5 feet
(1,100 ft2/8 ft = 137.5 ft).
4. Multiples of two raft hydroponic
tanks are required for the UVI
system. In this case only two
hydroponic tanks are required.
Therefore, the minimum length
of each hydroponic tank will be
68.75 feet (137.5 ft ÷ 2 = 68.75
ft). Since polystyrene sheets
come in 8-foot lengths, the total
number of sheets per hydropon-
ic tank will be 8.59 sheets (68.75
ft ÷ 8 ft/sheet = 8.59 sheets).
To avoid wasting material,
round up to nine sheets.
Therefore, the hydroponic tanks
will be 72 feet long (9 sheets ×8
ft per sheet = 72 ft).
5. The total plant growing area
will then be 1,152 ft2(72 ft ×8
ft per tank ×2 tanks = 1,152
ft2). This is equal to 107 m2
(1,152 ft2÷ 10.76 ft2/m2).
6. At a planting density of 29.3
plants/m2, a total of 3,135 plants
will be cultured in the system.
The extra plants will provide a
safety margin against mortality
and plants that do not meet
marketing standards.
7. Assume that a feeding rate of 60
g/m2/day provides sufficient
nutrients for good plant growth.
Therefore, daily feed input to
the system will be 6,420 g (60
g/m2/day ×107 m2= 6,420 g).
This is equal to 14.1 pounds of
feed (6,420 g ÷ 454 g/lb = 14.1
lb).
8. Annual feed input to the system
will be 5,146 pounds (14.1
lb/day ×365 days = 5,146 lb)
9. Assume the feeding conversion
ratio is 1.7. Therefore, the feed
conversion efficiency is 0.59 (1
lb of gain ÷ 1.7 lb of feed =
0.59).
10. The total annual fish produc-
tion gain will be 3,036 pounds
(5,146 lb ×0.59 feed conversion
efficiency = 3,036 lb).
11. Assume that the desired harvest
weight of the fish will be 500 g
(1.1 lb) and that 50-g (0.11-lb)
fingerlings will be stocked.
Therefore, individual fish will
gain 450 g (500 g harvest weight
- 50 g stocking weight = 450 g).
The weight gain per fish will be
approximately 1 pound (454 g).
12. The total number of fish har-
vested will be 3,036 (3,036 lb of
total gain ÷ 1 lb of gain per fish
= 3,036 fish).
13. Total annual production will be
3,340 pounds (3,036 fish ×1.1
lb/fish = 3,340 lb) when the ini-
tial stocking weight is considered.
14. If there are four fish-rearing
tanks and one tank is harvested
every 6 weeks, there will be 8.7
harvests per year (52 weeks ÷ 6
weeks = 8.7).
15. Each harvest will be 384 pounds
(3,340 lb per year ÷ 8.7 harvests
per year = 384 lb/harvest).
16. Final harvest density should not
exceed 0.5 pound/gallon.
Therefore, the water volume of
each rearing tank should be 768
gallons (384 lb ÷ 0.5 lb/gal =
768 gal). The tank should be larg-
er to provide a 6-inch freeboard
(space between the top edge of
the tank and the water levels).
17. Each fish requires 2.2 gallons of
water (1.1 lb ÷ 0.5 lb of fish/gal
= 2.2 gal per fish).
18. The stocking rate is 349 fish per
tank (768 gal ÷ 2.2 gal/fish =
349 fish).
19. To account for calculated mortali-
ty, the stocking rate (349 fish per
tank) should be increased by 35
fish (349 fish ×0.10 = 34.9) to
attain an actual stocking of 384
fish per tank.
In summary, two hydroponic tanks
(each 72 feet long by 8 feet wide) will
be required to produce 1,000 Bibb
lettuce plants per week. Four fish-
rearing tanks with a water volume of
768 gallons per tank will be required.
The stocking rate will be 384 fish per
tank. Approximately 384 pounds of
tilapia will be harvested every 6
weeks, and annual tilapia production
will be 3,340 pounds.
Economics
The economics of aquaponic systems
depends on specific site conditions
and markets. It would be inaccurate
to make sweeping generalizations
because material costs, construction
costs, operating costs and market
prices vary by location. For example,
an outdoor tropical system would be
less expensive to construct and oper-
ate than a controlled-environment
greenhouse system in a temperate cli-
mate. Nevertheless, the economic
potential of aquaponic systems looks
promising based on studies with the
UVI system in the Virgin Islands and
in Alberta, Canada.
The UVI system is capable of produc-
ing approximately 11,000 pounds of
tilapia and 1,400 cases of lettuce or
11,000 pounds of basil annually
based on studies in the Virgin
Islands. Enterprise budgets for tilapia
production combined with either let-
tuce or basil have been developed.
The U.S. Virgin Islands represent a
small niche market with very high
prices for fresh tilapia, lettuce and
basil, as more than 95 percent of veg-
etable supplies and nearly 80 percent
of fish supplies are imported. The
budgets were prepared to show rev-
enues, costs and profits from six pro-
duction units. A commercial enter-
prise consisting of six production
units is recommended because one
fish-rearing tank (out of 24) could be
harvested weekly, thereby providing
a continuous supply of fish for mar-
ket development.
The enterprise budget for tilapia and
lettuce shows that the annual return
to risk and management (profit) for
six production units is US$185,248.
The sale prices for fish ($2.50/lb) and
lettuce ($20.00/case) have been estab-
lished through many years of market
research at UVI. Most of the lettuce
consumed in the Virgin Islands is
imported from California. It is trans-
ported by truck across the United
States to East Coast ports and then
shipped by ocean freighters to
Caribbean islands. Local production
capitalizes on the high price of
imports caused by transportation
costs. Locally produced lettuce is also
fresher than imported lettuce.
Although this enterprise budget is
unique to the U.S. Virgin Islands, it
indicates that aquaponic systems can
be profitable in certain niche mar-
kets.
The enterprise budget for tilapia and
basil shows that the annual return to
risk and management for six produc-
tion units is US$693,726. Aquaponic
systems are very efficient in produc-
ing culinary herbs such as basil (Fig.
11) and a conservative sale price for
fresh basil with stems in the U.S.
Virgin Islands is $10.00/pound.
However, this enterprise budget is
not realistic in terms of market
demand. The population (108,000
people) of the U.S. Virgin Islands
cannot absorb 66,000 pounds of fresh
basil annually, although there are
opportunities for provisioning ships
and exporting to neighboring islands.
A more realistic approach for a six-
unit operation is to devote a portion
of the growing area to basil to meet
local demand while growing other
crops in the remainder of the system.
The break-even price for the
aquaponic production of tilapia in the
Virgin Islands is $1.47/pound, com-
pared to a sale price of $2.50/pound.
The break-even prices are $6.15/case
for lettuce (sale price = $20.00/case)
and $0.75/pound for basil (sale price
= $10.00/pound). The break-even
prices for tilapia and lettuce do not
compare favorably to commodity
prices. However, the cost of construc-
tion materials, electricity, water, labor
and land are very high in the U.S.
Virgin Islands. Break-even prices for
tilapia and lettuce could be consider-
ably lower in other locations. The
break-even price for basil compares
favorably to commodity prices
because fresh basil has a short shelf
life and cannot be shipped great dis-
tances.
A UVI aquaponic system in an envi-
ronmentally controlled greenhouse at
the Crops Diversification Center
South in Alberta, Canada, was evalu-
ated for the production of tilapia and
a number of plant crops. The crops
were cultured for one production
cycle and their yields were extrapo-
lated to annual production levels.
Based on prices at the Calgary whole-
sale market, annual gross revenue
was determined for each crop per
unit area and per system with a plant
growing area of 2,690 ft2(Table 2).
Figure 11. Basil production in the UVI
aquaponic system.
Table 2. Preliminary production and economic data from the UVI aquaponic system at the Crop
Diversification Center South, Alberta, Canada.1(Data courtesy of Dr. Nick Savidov)
Annual production Wholesale price Total value
Crop lb/ft2tons/2690 ft2Unit $ $/ft2$/2690 ft2
Tomatoes 6.0 8.1 15 lb 17.28 6.90 18,542
Cucumbers 12.4 16.7 2.2 lb 1.58 8.90 23,946
Eggplant 2.3 3.1 11 lb 25.78 5.33 14,362
Genovese basil 6.2 8.2 3 oz 5.59 186.64 502,044
Lemon basil 2.7 3.6 3 oz 6.31 90.79 244,222
Osmin basil 1.4 1.9 3 oz 7.03 53.23 143,208
Cilantro 3.8 5.1 3 oz 7.74 158.35 425,959
Parsley 4.7 6.3 3 oz 8.46 213.81 575,162
Portulaca 3.5 4.7 3 oz 9.17 174.20 468,618
1Ecomonic data based on Calgary wholesale market prices for the week ending July 4, 2003.
The information given herein is for educational purposes only. Reference to
commercial products or trade names is made with the understanding that
no discrimination is intended and no endorsement by the Southern Regional
Aquaculture Center or the Cooperative Extension Service is implied.
The work reported in this publication was supported in part by the Southern Regional Aquaculture Center
through Grant No. 2003-38500-12997 from the United States Department of Agriculture, Cooperative State
Research, Education, and Extension Service.
SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software Steering
Committee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have not
been revised are considered to reflect the current state of knowledge.
Annual production levels based on
extrapolated data from short produc-
tion cycles are subject to variation.
Similarly, supply and demand will
cause wholesale prices to fluctuate
during the year. Nevertheless, the
data indicate that culinary herbs in
general can produce a gross income
more than 20 times greater than that
of fruiting crops such as tomatoes
and cucumbers. It appears that just
one production unit could provide a
livelihood for a small producer.
However, these data do not show
capital, operating and marketing
costs, which will be considerable.
Furthermore, the quantity of herbs
produced could flood the market and
depress prices. Competition from
current market suppliers will also
lead to price reductions.
Overview
Although the design of aquaponic
systems and the choice of hydropon-
ic components and fish and plant
combinations may seem challenging,
aquaponic systems are quite simple
to operate when fish are stocked at a
rate that provides a good feeding
rate ratio for plant production.
Aquaponic systems are easier to
operate than hydroponic systems or
recirculating fish production systems
because they require less monitoring
and usually have a wider safety
margin for ensuring good water
quality. Operating small aquaponic
systems can be an excellent hobby.
Systems can be as small as an
aquarium with a tray of plants cov-
ering the top. Large commercial
operations comprised of many pro-
duction units and occupying several
acres are certainly possible if mar-
kets can absorb the output. The edu-
cational potential of aquaponic sys-
tems is already being realized in
hundreds of schools where students
learn a wide range of subjects by
constructing and operating aquapon-
ic systems. Regardless of scale or
purpose, the culture of fish and
plants through aquaponics is a grati-
fying endeavor that yields useful
products—food.
... However, a recent study [12] revealed that the aquaponic substrate technique assures the highest rate of return, compared to DWC and NFT techniques. Considering that, according to various research studies [8,10], the cost of substrate represents a significant percentage of total investment costs performed to integrate aquaponics into already existing RAS, several attempts have been made by other authors [44][45][46] in order to identify a suitable material which should accomplish both economic and environmental sustainability desideratum. Thus, some authors [47] tested crushed stone number 3 (CS) and flexible polyurethane foam (FPF) as substrates to produce lettuce, integrated into a tilapia RAS and revealed that the use of CS assures a larger number of leaves, higher nutrients concentrations and increase production of lettuce biomass. ...
... Other media grow beds used in aquaponics, as revealed by some authors [48] are light-expanded clay aggregate (LECA), perlite or pumice, used both for root support and microbial substrate. Also, other authors [45] characterized substrate grow beds as sand and gravel as the most labor-intensive and highly exposed to clogging due to the deposition of detritus. Also, a recent research study [45] revealed that if increasing the production density of fish, most of the cultured crops tended to grow better if substrate aquaponics techniques is used, compared to DWC and NFT. ...
... Also, other authors [45] characterized substrate grow beds as sand and gravel as the most labor-intensive and highly exposed to clogging due to the deposition of detritus. Also, a recent research study [45] revealed that if increasing the production density of fish, most of the cultured crops tended to grow better if substrate aquaponics techniques is used, compared to DWC and NFT. Other GM which has been tested for aquaponic plant growth are volcanic stone, ceramic pellets, ceramic rings and nanorods [49] and, as a result, it had been concluded that nanorods GM experimental variant recorded the best results both in terms of plant growth and nutrients removal. ...
Article
Full-text available
Here, we aim to improve the overall sustainability of aquaponic basil (Ocimum basilicum L.)-sturgeon (Acipenser baerii) integrated recirculating systems. We implement new AI methods for operational management together with innovative solutions for plant growth bed, consisting of Rapana venosa shells (R), considered wastes in the food processing industry. To this end, the ARIMA-supervised learning method was used to develop solutions for forecasting the growth of both fish and plant biomass, while multi-linear regression (MLR), generalized additive models (GAM), and XGBoost were used for developing black-box virtual sensors for water quality. The efficiency of the new R substrate was evaluated and compared to the consecrated light expended clay aggregate-LECA aquaponics substrate (H). Considering two different technological scenarios (A-high feed input, Blow feed input, respectively), nutrient reduction rates, plant biomass growth performance and additionally plant quality are analysed. The resulting prediction models reveal a good accuracy, with the best metrics for predicting N-NO3 concentration in technological water. Furthermore, PCA analysis reveals a high correlation between water dissolved oxygen and pH. The use of innovative R growth substrate assured better basil growth performance. Indeed, this was in terms of both average fresh weight per basil plant, with 22.59% more at AR compared to AH, 16.45% more at BR compared to BH, respectively, as well as for average leaf area (LA) with 8.36% more at AR compared to AH, 9.49% more at BR compared to BH. However, the use of R substrate revealed a lower N-NH4 and N-NO3 reduction rate in technological water, compared to H-based variants (19.58% at AR and 18.95% at BR, compared to 20.75% at AH and 26.53% at BH for N-NH4; 2.02% at AR and 4.1% at BR, compared to 3.16% at AH and 5.24% at BH for N-NO3). The concentration of Ca, K, Mg and NO3 in the basil leaf area registered the following relationship between the experimental variants: AR > AH > BR > BH. In the root area however, the NO3 were higher in H variants with low feed input. The total phenolic and flavonoid contents in basil roots and aerial parts and the antioxidant activity of the methanolic extracts of experimental variants revealed that the highest total phenolic and flavo-noid contents were found in the BH variant (0.348% and 0.169%, respectively in the roots, 0.512% and 0.019%, respectively in the aerial parts), while the methanolic extract obtained from the roots of the same variant showed the most potent antioxidant activity (89.15%). The results revealed that an analytical framework based on supervised learning can be successfully employed in various Citation: Petrea, Ș.-M.; Simionov, I.A.; Antache, A.; Nica, A.; Oprica, L.; Miron, A.; Zamfir, C.G.; Neculiță, M.; Dima, M.F.; Cristea, D.S. An Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses /by/4.0/). Plants 2023, 12, 540 2 of 50 technological scenarios to optimize operational management in an aquaponic basil (Ocimum basili-cum L.)-sturgeon (Acipenser baerii) integrated recirculating systems. Also, the R substrate represents a suitable alternative for replacing conventional aquaponic grow beds. This is because it offers better plant growth performance and plant quality, together with a comparable nitrogen compound reduction rate. Future studies should investigate the long-term efficiency of innovative R aquaponic growth bed. Thus, focusing on the application of the developed prediction and forecasting models developed here, on a wider range of technological scenarios.
... The treatment units can eliminate the fish waste that are contained in the water effluent, e.g. ammonium (NH 4 ), carbon dioxide (CO 2 ), and organic carbon (Badiola et al., 2012;Rakocy et al., 2006). The large-scale introduction of RAS, however, is limited because of its high capital investment and operational cost. ...
... Another improvement of microalgal N and P retention can also be carried out by the solid waste mineralization, which is correlated with feed composition (Amirkolaie, 2011). The mineralized solid waste then can be taken up by the microalgae (Rakocy et al., 2006). If the operational parameters that were used in this study are maintained, microalgal N and P retention can be improved by using larger membrane area. ...
Thesis
A recirculation aquaculture system (RAS) is an aquaculture facility that reuses and recirculates 90-99% water. The water is processed through several treatment steps to maintain good water quality for fish growth. However, RAS still has constraints due to its high capital investment and operational cost. RAS can potentially be integrated with a microalgal biofilm to convert fish waste into harvestable products to minimize operational costs. The microalgal biofilm, which is adhered to the carrying cloth that floats on the water due to the buoyancy, could provide easy and low-cost microalgal biomass harvesting and prevention of microalgal biomass carried away into the fish-rearing unit. This study aims to assess the feasibility of integrating a microalgal biofilm unit within a RAS to maintain good water quality and recover nutrients as microalgal biomass through a model simulation and a pilot-scale experiment. The model was developed based on the mass balances of nutrients in the separate unit operations involved. Separate models were developed to complete the mass balances model, consisting of fish feed and waste production, nutrients removal in the biofilter, and microalgal biofilm growth model. The model development and simulation were carried by using Mathcad 15.0 software. The variation of several operational parameters, i.e., light intensity, water flow under the membrane, and microalgal biomass harvesting frequency, were tested through simulation regarding their effect on microalgal biofilm nutrient uptake rate. The simulation showed that the increase of light intensity improved the nutrients uptake rate by the microalgal biomass. The improvement of nutrients uptake rate stopped eventually when the operation switched from light-limited into diffusion-limited. The increase of water velocity under the membrane also elevated the nutrient uptake rate due to diffusion limitation reduction. However, the nutrient uptake rate stabilized in higher water velocity since the uptake rate was limited by the constant light intensity and the remaining diffusion limitation through the membrane and the microalgal biofilm. The more frequent the microalgal biomass harvested, the earlier the maximum nutrient uptake rate can be attained. A thin microalgal biofilm, due to frequent harvesting, had less diffusion resistance. However, too frequent harvesting must also be avoided since a very thin microalgal biofilm layer cannot absorb all the light. This condition will lead to the loss of a considerable amount of light which is undesirable. In the pilot-scale experiment, Chlorella sorokiniana and Clarias gariepinus were used as the model organisms. The fish were fed at 4.63 g-feed.kg-fish-1.day-1 specific feeding rate. The pilot-scale recirculation system, with a total volume of 388 L, was operated for 30 days. The water quality was monitored daily. The water quality, microalgal biomass, and fish were measured and analyzed. The pilot-scale experiment showed that the RAS+microalgal biofilm system maintained the water quality under the optimum/tolerable condition for the fish growth. The microalgal biofilm grew using the nutrients from the fish waste, where the average biomass productivity of 4.9 g.m-2.day-1 was achieved. The N and P uptake by the microalgal biofilm were 0.36 g-N.m-2.day-1 and 0.06 g-P.m-2.day-1 respectively. Based on the nitrogen balances, 22% of the metabolic fish waste can be reused as fish feed through microalgal biomass assimilation. Based on the results, the integration of RAS+microalgal biofilm is feasible since the good water quality for fish growth was maintained. This study showed the proof of concept that the integration of RAS and microalgal biofilm can potentially be applied since the fish waste was taken up by the microalgal biofilm and converted into biomass that can be further harvested. It was also shown that diffusion resistance in the microalgal biofilm system layers is the main limitation regarding fish waste uptake by the microalgal biofilm. This limitation can be overcome by improving the operational parameters, e.g., by applying light intensity of 200-400 μmol-ph.m-2.s-1 and water velocity beneath the microalgal biofilm membrane of more than 1.8 x 10-3 m.s-1. Some other recommendations and further studies, e.g., water N:P ratio adjustment and longer experiment duration, can also be carried out to improve the feasibility of RAS+microalgal biofilm integration.
... That is the resultant impact. Rakocy et al. (2006) added that the acceptable limit of dissolve oxygen is 5, though. The DO in the NFT system is within the range that permits the fish and lettuce to develop properly. ...
... The increase in the nitrogen-base compounds in the NFT system is due to the gradual build up of ammonia due to the microbiological activity on the left over of fishes feed and their faeces that were later converted to nitrate and nitrite via bacterial nitrification. At the point to observation continuous introduction of clean water and dislodging the NFT system reduce the negative consequence of the compound on the growth of fishes and the lettuce(Rakocy et al., 2006). ...
Article
Full-text available
Aquaponics as a key factor in the advancement of integrated food production systems and noted potential by simultaneous combination of aquaculture and hydroponics practice. This study evaluate a nutrient film aquaponics system (NFT) for catfish and lettuce. The catfish was raised under different feeding rate treatment: 5% (TRT5%) and 3% (TRT3%). The lettuce was grown with the water from the two treatments and the convectional method (control). The observation were taken in seventh days after transplanting for 4 weeks. The effect of the treatments and water quality on the growth and yield parameters of lettuce were analyzed using analysis of variance and regression analysis at 5% significance level. The result shows that the initial weight of the stocked fish under different treatment tanks had no significant difference (P<0.05). In 3-10th weeks, TRT5% is significantly (P<0.05) higher than the TRT3%. The TRT5% significantly increased the leaf number and plant height of the lettuce by 27.38% and 28.72% respectively con. The TRT3% significantly increased the leaf number and plant height of the lettuce by 13.10% and 12.34% respectively. The developed mathematical models for number of leaf, plant height, leaf area, weight and productivity had an accuracy of93.2%, 95.6%, 99.7%, 98.28% and 83.32% respectively, Therefore, it should be adopted by small and medium scale aquaponics farmer for significant prediction on lettuce yield as a function of NFT water quality.
... In present study, the organic waste volume generated trial seems that has not provided adequate nutrition for lettuce. Leaves number, total fresh mass, and yield of the lettuce varieties studied were relatively superior that the values reported by Sikawa andYakupitiyage (2010); however, were lower than the values reported for aquaponics systems using e uent enriched with a nutrient solution (Seawright et al., 1998;Rakocy et al., 2006). In addition, interactions between sh stocking density and leaf number, total fresh mass, and yield of lettuces were found here. ...
Preprint
Full-text available
This study investigated the growth performance parameters and parasites of Colossoma macropomum farmed in an aquaponic system constructed semi-dry wetland. Fingerling of C. macropomum (8.3 ± 0.9 g) were stocked in three experimental densities: 334, 668 and 1,002 g m − 3 g using four replicates by each treatment. The initial weight of C. macropomum was similar between fish densities tested. Electrical conductivity, nitrite, nitrate, potassium, and magnesium, turbidity, phosphate, total ammonia, and alkalinity increased with fish density. Dissolved oxygen concentrations showed a reduction, reflecting on fish growth. The final weight was different and that it was negatively impacted with increased density. The specific growth rate was similar between treatments with 334 and 668 g m − 3 , but it differed significantly from treatment with and 1,002 g m − 3 of fish. The mean weight gain decreased with increased of fish density, while feed conversion ratio increased. Relative condition factor and survival of fish were not affected by the densities of fish. Ichthyophthirius multifiliis , Anacanthorus spathulatus , Notozothecium janauachensis and Mymarothecium boegeri were parasites found on C. macropomum gills in low abundance, which was not influenced by different densities of fish. Our results showed that fish yield was negatively impacted with increased density and differed between the by different density of fish, while the sanity was not affected.
... Aquaponics is the combination of hydroponics (plants without soil) and aquaculture (fish in a recirculating system). In aquaponics, wastewater of the fish tank is used to fertilize hydroponics production beds beside plant roots, and associated rhizosphere bacteria clean up the water from nutrients, especially ammonia as a toxic element to fish (Rakocy et al., 2006;Graber and Junge, 2009;Rakocy, 2012). In this study, two different fish stocking densities of red tilapia were examined in order to investigate its effects on mint growth in a medium-scale production. ...
Article
Full-text available
This study determined how stocking density affected water quality, red tilapia performance, proximate body composition, and mint performance in low-saline aquaponic systems. Experimental systems were stocked with 40 fish / m3 (low density: LD) and 60 fish/ m3 (high density: HD), three replicates each. The experiment lasted for 120 days. Dissolved Oxygen (mg/l) was significantly higher in LD treatment. Water pH decreased significantly (P<0.05) with increasing stocking density. Both Ammonia nor Nitrite did not affect significantly. Weight gain and specific growth rate% were significantly higher in the LD group, 150.33 ±8.95 and 1.65 ±0.006, respectively, as compared with 122.0 ± 3.46 and1.48 ± 0.005 for HD. The survival rate% was 92.5%±1.25 and 88.33%±0.98 for LD and HD, respectively. Total fish biomass in HD units (8.78 Kg. ± 0.24) was significantly higher than in LD (7.18 Kg. ± 0.37). The feed conversion ratio was significantly reduced with increasing stocking density, whereas the protein efficiency ratio increased with stocking density. Individual plant fresh weight, length, and a number of leaves did not differ significantly with fish density. Root length significantly declined with fish density increasing 60.21±4.79 and 41.18 ± 4.20 cm, respectively. The fish body content of moisture, protein, and ash did not differ significantly with stocking density. Significantly lower fish body fat content was found in the HD group
... Meanwhile, the aquaponic technique produces crops and raises fish without relying on toxic chemical pesticides, synthetic fertilizers, genetically modified seeds, or practices that degrade soil, water, or other natural resources. More specifically, aquaponics is a hybrid food technology system that has the potential to remove the negative environmental impact of current farming techniques [154]. This system is a valuable alternative to both traditional agriculture, fishing, and fish farming. ...
Article
Full-text available
Aquaculture is an important component of the human diet, providing high-quality aquatic food for global or local consumption. Egypt is one of the countries most vulnerable to the potential impacts of climate change (CC), especially in the aquaculture sector. CC is one of the biggest challenges of our time and has negatively affected different water bodies. CC leads to the combination of changes in water availability, a decrease in water quality, the movement of salt water upstream due to rising sea levels, and the salinization of groundwater supplies will threaten inland freshwater aquaculture. Similarly, higher temperatures resulting from CC lead to reduce dissolved oxygen levels, increased fish metabolic rates, increased risk of disease spread, increased fish mortality, and consequently decreased fish production. CC may also indirectly affect aquaculture activities; for example, large areas of lowland aquaculture ponds can be highly vulnerable to flooding from rising sea levels. Thus, the current overview will briefly discuss the state of the aquaculture sector in Egypt, the meaning of CC, its causes, and its effects on the different elements of the aquaculture sector, and finally, we will review the appropriate ways to mitigate the adverse effects of CC on fish farming, especially in Egypt.
... Dissolved nitrogen is transformed in the biofilter, mainly into nitrates and nitrites. In this form, nitrogen is easily assimilated by plants and can be used as a fertilizer in agriculture or can be removed in treatment ponds with plants or root zones 5,18,21 . ...
Chapter
Basil or sweet basil is named Ocimum basilicum L. from the Lamiaceae family, which originated from India, and it is also well known as a culinary herb in other countries such as Italy, Thailand, Vietnam, and Taiwan. Agricultural systems (traditional or alternative agricultural systems) have a different effect on the morphology, yield, and yield components of basil. These agricultural systems include aquaponics and hydroponics systems and organic farming by using organic manure as vermicompost, poultry or cattle manure, biofertilizer, growing techniques, etc., as well as chemical fertilizer. Fertilization, especially organic and chemical fertilizer, combined with minerals, applied in appropriate dose and composition, affects growth, herb weight, and basil inorganic matter content. In this context, the management of the fertilizers is a significant factor to obtain successful basil cultivation and sustainable agriculture. So, the best agricultural system and growing condition should be determined to obtain the maximum yield values in basil. In this chapter, botany, distribution, origin, domestication, spread, genetic resource, collection, conservation, characterization, and evaluation (different agricultural systems, fertilizer application, genetic variability and morphology, and yield properties) will be covered in detail and provide information for basil producers and researchers.
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